Characterization of Motor Neuron Prostaglandin E2 EP3 Receptor Isoform in a Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a motor neuron disease with adult onset, characterized by progressive loss of motor neurons. Prostaglandin E2 (PGE2), a lipid mediator, exerts its biological functions by binding to four subtypes of E-prostanoid (EP1-4). Among them, EP3 has been shown to have multiple isoforms, EP3 alpha, EP3 beta, and EP3 gamma, produced by alternative splicing. Since PGE2 has been shown to have important pathophysiological roles in ALS, experiments were performed to identify EP3 receptor isoform(s) in spinal motor neurons of wild-type (WT) and ALS model (G93A) mice. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of adult mice demonstrated expression of EP3 alpha and EP3 gamma mRNAs in the lumbar spinal cord, whereas EP3 beta mRNA was barely detectable. Laser capture microdissection was used to dissect out motor neurons from frozen samples of lumbar spinal cord in these mice for analysis by real-time PCR. We found that expression of EP3 gamma mRNA was predominant in these neurons, whereas EP3 alpha and EP3 beta mRNAs were undetectable. At the early symptomatic stage, the mRNA expression profiles of these splice isoforms in G93A motor neurons were comparable to those in neurons from WT mice. These results suggest that the PGE2-to-EP3 signaling pathway is mediated mainly by the EP3 gamma isoform in the motor neurons of mice, and that modulation of the EP3 gamma isoform in motor neurons may be a promising new therapeutic approach for ALS.